(1) Field of the Invention
The present invention lies in the field of fluid temperature control installations on board aircraft, and more particularly rotorcraft. Taken generally, such installations comprise a variety of systems for applying temperature control to a fluid, in particular a system for cooling a main power plant of the rotorcraft and a system for temperature control of air inside the cabin of the rotorcraft.
(2) Description of Related Art
Aircraft are fitted with a fluid temperature control installation that is made of various systems for controlling the temperature of a fluid, which systems are dedicated to respective particular functions. Overall, the installation should be considered as grouping together various circuits for conveying a fluid that is subjected to temperature control. The ways in which temperature control systems are organized depend on their respective functions and on the natures of the fluids that each of them uses.
Aircraft, and in particular rotorcraft, have a main power plant providing lift and/or propulsion. Such a power plant comprises in particular at least one engine member engaged with a main gearbox that is driven by the engine member. The main gearboxes are used for driving both propulsive members of the aircraft and also accessories with which the aircraft is fitted. Specific transmission systems for driving various pieces of equipment of the aircraft may be driven by the main gearbox or by secondary gearboxes that are respectively associated therewith, or indeed by respective individual motor members that are powered electrically from the network on board the aircraft.
More particularly with rotorcraft, the main power plant is used for driving one or more rotors of the rotorcraft and possibly also propulsive propellers in hybrid helicopters. The rotors and/or propulsive propellers are driven in rotation by the main gearbox so as to achieve at least lift if not also propulsion and/or guidance of the rotorcraft. By way of example, the engine member may be a diesel engine or a turbine engine, or any other engine member suitable for developing power for driving at least the rotors and/or the propulsive propellers in rotation, and possibly also accessories or equipment of the rotorcraft.
The gearbox should be considered as being a member of the aircraft that is interposed between the engine member and a member that is to be driven, without that specifying the particular organization and/or function of the member that is to be driven or the ways in which the gearbox is included in the transmission system of the rotorcraft. Gearboxes, and in particular main gearbox (MGB), are subjected in operation to temperature rises that need to be controlled. It should be considered that gearbox covers any member that is subjected to drive and that needs its temperature to be controlled.
For this purpose, the fluid temperature control installation comprises a system for cooling one or more gearboxes. Such a cooling system comprises at least one closed circuit for circulating a fluid that is to be cooled, usually in the liquid state, between the gearbox and a heat exchanger. The fluid for cooling is commonly a lubricant that flows from the gearbox to the heat exchanger in order to lower the temperature of the fluid for cooling, and then from the heat exchanger to the gearbox in order to cool the gearbox.
The heat exchanger is commonly arranged as a radiator or an analogous member for exchanging heat between a stream of air and the fluid for cooling. The heat exchanger comprises an internal circuit for passing a flow of the fluid for cooling and a heat exchange structure of the type having fins or the like for exchanging heat with a stream of cooling air. The heat exchanger has an airflow generator member for generating a flow of cooling air that passes through the heat exchange structure. Such an airflow generator member is commonly arranged as a propeller type fan that, under motor drive, serves to generate a stream of air and to drive the stream of air through the heat exchanger.
Those kinds of organization for a system for cooling a gearbox are conventional in the general field of vehicles. The use of such cooling systems for a rotorcraft present drawbacks, in particular in terms of energy losses and difficulties associated with safe installation on board the rotorcraft.
For example, concerning the airflow generator member, the energy needed for driving it is defined as being constant with respect to optimized needs for cooling the heat exchanger. In a rotorcraft in particular, such optimized needs are defined relative to a situation in which the rotorcraft is performing hovering flight and/or a situation in which temperatures outside the rotorcraft are high. This leads to energy being lost in other situations in which the rotorcraft might be placed, given that the airflow generator member is driven so as to consume a constant level of power. This leads to significant loss of energy in a cruising flight situation and/or in a situation where temperatures outside the rotorcraft are low. In such situations, the cooling needs of the main transmission do not require power to be consumed at such a constant level.
It is also desirable for the airflow generator member of the cooling system to be driven by power taken from the main transmission so as to avoid taking electricity from the on-board electricity network and so as to avoid lengthening the closed circuit considerably. The proximity between the airflow generator member and the main gearbox makes it difficult to install the airflow generator member in a zone of the rotorcraft that houses power members, with constraints in terms of safety and making the operation of the airflow generator member reliable.
Aircraft also include a cabin in which the air needs to be temperature-controlled. The term “cabin” is used to cover any space in the aircraft for accommodating people and/or cargo. Controlling the temperature of cabin air seeks to provide comfort for the passengers and/or to preserve cargo, and relates in particular to a function of heating, ventilation, and/or air conditioning the cabin.
For this purpose, the fluid temperature control installation includes a system for temperature controlling the ambient air in the cabin. The temperature control of cabin air involves in particular an open circuit for conveying and/or applying temperature control to various streams of air, having a plurality of air circuits in association.
In one embodiment, the system for temperature controlling cabin air comprises one or more independent heating, ventilation, and/or air conditioning devices. Such independent devices are powered electrically from the on-board network and they are located inside the cabin.
In a more complex embodiment, the cabin air temperature control system advantageously takes advantage of a heat source coming from the main power plant for heating ambient air in the cabin. Such a source provides heat that is extracted in particular from a main compressor of the main power plant, specifically when the engine member is a turboshaft engine. In such an embodiment, the cabin air temperature control system has a plurality of air circuits distributed over the rotorcraft.
A first air circuit is a circuit for taking hot air from the main compressor to at least one air temperature control device. The first air circuit has one or more ducts for conveying hot air from the main compressor to the air temperature control device placed as close as possible to the cabin.
A second air circuit is a circuit for taking fresh air by force from outside the rotorcraft and for conveying the fresh air that has been taken to the air temperature control device. Fresh air is taken using an airflow generator member placed inside the second air circuit. Such an airflow generator member is commonly of the type arranged as a propeller fan that is electrically powered from the on-board network of the rotorcraft. The second air circuit is advantageously used for ventilating the cabin, by being in air-flow communication with an auxiliary air circuit dedicated to this function. The auxiliary air circuit admits outside fresh air from the second air circuit directly into the cabin.
The air temperature in the cabin is controlled by performing selective mixing within the air temperature control device between outside fresh air and hot air coming from the main compressor. The air temperature control device includes an air mixer having an ejector for ejecting the hot air from the first air circuit, and an opening for admitting fresh air from the second air circuit. Air temperature control means achieve selective admission of hot air and of outside fresh air into the mixer as a function of requirements for moderate-temperature air that is exhausted from the air temperature control device to the cabin.
The use of various cabin air temperature control systems presents drawbacks, in particular in terms of energy losses, sound nuisance, and/or difficulties associated with installing such systems safely in the rotorcraft.
For example, concerning energy losses, the independent heating, ventilation, and/or air conditioning devices consume a large fraction of the electrical energy of the rotorcraft, which should be avoided.
Also by way of example, for air temperature control systems using hot air produced by the main power plant, these lead in particular to sound nuisance and to difficulties of safe incorporation in the rotorcraft.
The sound nuisance stems from the hot air ejector for ejecting hot air from the main compressor and leading into the air mixer. Such sound nuisance stems from the expansion of the compressed hot air that is released into the mixer. Such a drawback is known, and reference may be made to document U.S. Pat. No. 6,139,423 (Sikorsky Aircraft Corp.) that proposes a solution for attenuating such sound nuisance.
Safe incorporation of ducts for conveying hot air from the main compressor to the temperature control device is difficult. Such ducts extend along the fuselage of the rotorcraft and account needs to be taken of the high temperature of the air that they convey in order to ensure that the ducts are installed safety in the rotorcraft.
In general, it is found that the fluid temperature control installations on board aircraft, in particular rotorcraft, need to be improved, in particular in terms of energy losses, of the safety of their installation, and/or in terms of any sound nuisance to which they might lead. Such installations also need to be improved by simplifying their structure and their modes of operation as much as possible, without affecting their effectiveness or their safe installation on board the rotorcraft. It is also desirable to optimize reduction in the cost of obtaining them and installing them on board the aircraft, and also their maintenance costs.